π Berry phase and Zeeman splitting of Weyl semimetal TaP.

J Hu,D J Adams,I Chiorescu,J Y Liu,L Spinu,S M A Radmanesh,Z Q Mao,A Chuang,Y Wang,D Graf,J Wei

doi:10.1038/srep18674

Abstract

The recent breakthrough in the discovery of Weyl fermions in monopnictide semimetals provides opportunities to explore the exotic properties of relativistic fermions in condensed matter. The chiral anomaly-induced negative magnetoresistance and π Berry phase are two fundamental transport properties associated with the topological characteristics of Weyl semimetals. Since monopnictide semimetals are multiple-band systems, resolving clear Berry phase for each Fermi pocket remains a challenge. Here we report the determination of Berry phases of multiple Fermi pockets of Weyl semimetal TaP through high field quantum transport measurements. We show our TaP single crystal has the signatures of a Weyl state, including light effective quasiparticle masses, ultrahigh carrier mobility, as well as negative longitudinal magnetoresistance. Furthermore, we have generalized the Lifshitz-Kosevich formula for multiple-band Shubnikov-de Haas (SdH) oscillations and extracted the Berry phases of π for multiple Fermi pockets in TaP through the direct fits of the modified LK formula to the SdH oscillations. In high fields, we also probed signatures of Zeeman splitting, from which the Landé g-factor is extracted.

Highlights

In Dirac semimetals, the discrete band touching points near the Fermi level - the Dirac nodes - are protected from gap opening by crystalline symmetry
Unlike the well-established π Berry phase in Dirac systems as mentioned above[25,26,27,28,29,30,31], the experimental determination of Berry phase using the LL fan diagram remains elusive for monopnictide Weyl semimetals
We find that electrons from multiple Fermi pockets have π Berry phases accumulated along their cyclotron orbits, which agrees well with the nature of Weyl fermions

Summary

Introduction

In Dirac semimetals, the discrete band touching points near the Fermi level - the Dirac nodes - are protected from gap opening by crystalline symmetry. A non-zero Berry phase reflects the existence of band touching point such as Dirac nodes, and manifest itself in observable effects in quantum oscillations. The cyclotron motion (that is, closed trajectory in momentum space) of Dirac fermions under magnetic field B induces Berry phase that changes the phase of quantum oscillations. Unlike the well-established π Berry phase in Dirac systems as mentioned above[25,26,27,28,29,30,31], the experimental determination of Berry phase using the LL fan diagram remains elusive for monopnictide Weyl semimetals. If one oscillation frequency is close to another (which is commonly seen in these systems for some certain field orientations17,20,32), separating the individual peak requires high magnetic field which was not achieved in previous low field studies[14,15,16,19,20]

Methods

Results

Conclusion